I. Field of the Invention
The present invention relates generally to communications, and more specifically, to decoding preambles transmitted on preamble channels.
II. Background
The field of wireless communications has many applications including, e.g., cordless telephones, paging, wireless local loops, personal digital assistants (PDAs), Internet telephony, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. (As used herein, the term “cellular” encompasses both cellular and personal communications services (PCS) frequencies.) Various over-the-air interfaces have been developed for such cellular telephone systems including, e.g., frequency division multiple access (FDMA), time division multiple access (TDMA), and code division multiple access (CDMA). In connection therewith, various domestic and international standards have been established including, e.g., Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM), and Interim Standard 95 (IS-95). In particular, IS-95 and its derivatives, IS-95A, IS-95B, ANSI J-STD-008 (often referred to collectively herein as IS-95), and proposed high-data-rate systems for data, etc. are promulgated by the Telecommunication Industry Association (TIA), the International Telecommunications Union (ITU), and other well known standards bodies.
Cellular telephone systems configured in accordance with the use of the IS-95 standard employ CDMA signal processing techniques to provide highly efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assigned to the assignee of the present invention and fully incorporated herein by reference. An exemplary described system utilizing CDMA techniques is the cdma2000 ITU-R Radio Transmission Technology (RTT) Candidate Submission (referred to herein as cdma2000), issued by the TIA. The standard for cdma2000 is given in draft versions of IS-2000 and has been approved by the TIA. The cdma2000 proposal is backwards compatible with IS-95 systems. Another CDMA standard is the W-CDMA standard, as embodied in 3rd Generation Partnership Project “3GPP”, Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.
In the CDMA systems introduced above, voice and data traffic can be carried in message frames of various lengths. Typically, a remote station in the range of a base station must receive and decode a plurality of message frames in order to determine the complete voice and data payload information. Preambles are attached to the message frames to convey information as to the number of message frames that will carry a given payload. In addition to the number of frames that are needed to carry the full payload, preambles can also carry information identifying the target destinations and the transmission rates of the message frames. Other information, such as the radio link protocol (RLP) sequence numbers of the message frames, can also be included. Hence, the accurate decoding of message frames is dependent upon the detection and decoding of the preambles attached to said message frames. It is desirable to increase the ability of a target station to accurately detect and decode preambles, which would lead to more accurate detection and decoding of payload information.